1. Field of the Invention
This invention relates to an ophthalmic photographing apparatus, and more particularly, to an ophthalmic photographing apparatus in which the fundus of an eye to be examined is to be photographed with the angle of view changed, reduction in quantity of photographing light during narrow angle (high magnification) photography as compared with during wide angle (low magnification) photography is compensated for and which can photograph eyes even having small pupil diameters, by narrow angle photography.
2. Description of the Prior Art
In eye-fundus cameras, it is known to provide a ring slit opening in a system for illuminating an eye to be examined at a position optically substantially conjugate with the pupil of the eye to be examined, illuminate the eye from the area around the pupil thereof through a ring slit opening image formed in the pupil of the eye, and effect photographing by taking out the reflected light from the fundus of the eye from the central area of the pupil by the use of an apertured mirror for branching off the illuminating system and the photographing system.
This prevents light reflected by the cornea of the illuminating light, from entering the photographing system. Further, in eye-fundus cameras according to the prior art, it is known to provide a circular height-intercepting plate (i.e., a baffle) at a position optically subtantially conjugate with the crystalline lens of the eye in the system for illuminating the eye, and to prevent the light reflected by the crystalline lens, of the illuminating light, from entering the photographing system.
In such an eye-fundus camera having a ring slit and a baffle in the illuminating system during variable magnification photography, the sizes of the ring slit and the baffle have heretofore been constant irrespective of a magnification change and correspondingly, the sizes of the ring slit image and baffle image in the eye have also been constant.
Now, to photograph the fundus of an eye at a variable magnification, in addition to a case where a lens system provided in the photographing optical path which does not overlap the illuminating optical path, that is, a lens system provided in the photographing optical path subsequent to the apertured mirror, is varied, there is a case where an objective lens provided in the photographing optical path which overlaps the illuminating optical path is varied. An eye-fundus camera which has a ring slit and a baffle in the illuminating system and which effects variable magnification photography with the objective lens changed is known, and in such camera, during a magnification change, the ring slit has been replaced by another ring slit of a different size.
However, this camera is such that the size of the ring slit image or the like is made constant in the eye to be examined irrespective of interchange of the objective lens. That is, in the example of the prior art, it has not been practiced to change the size of the ring slit image during variable magnification photography.
Therefore, in the example of the prior art, the slit width of the ring slit image which is a window for introducing the illuminating light therethrough is fixed irrespective of a magnification change and thus, during narrow angle photography, as compared with during wide angle photography, the absolute quantity of photographing light is reduced.
There has also been a disadvantage that eyes to be examined having small pupil diameters cannot be photographed. That is, even if wide angle photography is changed over to narrow angle photography for an eye having a small pupil diameter, it is difficult, owing to the deficiency of the quantity of light, to judge the eye-fundus image and generally, the diameter of the pupil to be photographed is limited by the diameter during wide angle photography. Therefore, as compared with an ordinary narrow angle fixed photography camera. The diameter of the pupil to be photographed unavoidably becomes great during narrow angle photography and thus, eyes having small pupil diameters cannot be photographed.
Another method than the method described above, it would come to mind to increase the output of a photography flash to increase the quantity of photographing light during narrow angle photography, but in this case, it would be necessary to enlarge the capacity of the capacitor of the flash to increase the electrical energy.